Prior to setting forth a short discussion of the related art, it may be helpful to set forth definitions of certain terms that will be used hereinafter.
The term “MIMO” as used herein, is defined as the use of multiple antennas at both the transmitter and receiver to improve communication performance. MIMO offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the transmit power over the antennas to achieve spatial multiplexing that improves the spectral efficiency (more bits per second per Hz of bandwidth) or to achieve a diversity gain that improves the link reliability (reduced fading), or increased antenna directivity.
The term “beamforming” sometimes referred to as “spatial filtering” as used herein, is a signal processing technique used in antenna arrays for directional signal transmission or reception. This is achieved by combining elements in the array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.
The term “beamformer” as used herein refers to RF circuitry that implements beamforming and usually includes a combiner and may further include switches, controllable phase shifters, and in some cases amplifiers and/or attenuators.
The term “Receiving Radio Distribution Network” or “Rx RDN” or simply “RDN” as used herein is defined as a group of beamformers as set forth above.
The term “hybrid MIMO RDN” as used herein is defined as a MIMO system that employ two or more antennas per channel (N is the number of channels and M is the total number of antennas and M>N). This architecture employs a beamformer for each channel so that two or more antennas are combined for each radio circuit that is connected to each one of the channels.
In implementing RDNs, application specific integrated circuits (ASICs) are sometimes used for routing RF signals coming from the antennas to the radio circuits from which they are then conveyed to the baseband modules. ASIC RF routing modules are considered a good design choice due to their low loss, low cost, high Reliability. ASIC design however usually requires preliminary interface definition, and once done, flexibility to interfaces modifications is limited.
FIG. 1 depicts a K input RF beamformer. While K inputs is the maximum, one may use only part of the inputs (for instance, when the implementation provides lower number of inputs); that however comes at the price of combining losses, generated by imbalanced inputs or lack of some of them.
FIG. 2 depicts an N branch RDN with K antennas each. Another level of flexibility may be required vis-à-vis the number of radios fed by an RDN.
It would be therefore advantageous to provide an RF routing module for a Hybrid MIMO RDN architecture that is both variable in the number of connected antennas and the number of MIMO channels while keeping combiner losses at bay.